Fatty acids are widely utilized as an intermediate raw material of foods, such as a monoglyceride and a diglyceride, as well as an additive, and an intermediate raw material for other sorts of industrial products. These fatty acids are generally produced by hydrolyzing a vegetable oil such as a rapeseed oil, a soybean oil, a sunflower oil, a palm oil, or an animal oil such as beef tallow, using a high pressure method, or a decomposition method with an enzyme.
However, fatty acids produced simply by hydrolyzing an animal oil or a vegetable oil as described above, which have natural fatty acid compositions, are not necessarily suitable as a basic raw material for industrial use. In other words, it is necessary to fractionate unsaturated fatty acids and saturated fatty acids depending on the utilization purpose.
Therefore, it becomes necessary to modify a fatty acid composition to obtain a desired mixture of fatty acids. Generally in the fractionation process of fatty acids, a fractionation process using a solvent and a fractionation process using a wetting agent are employed. Although these processes show high efficiencies (e.g. yields) of separation, they pose problems such as an initial cost for facility investment as well as a high running cost for recovery of the solvent or the aqueous solution of the wetting agent and the like. In contrast, a dry fractionation process without using any solvent (e.g. a no solvent process) is an inexpensive fractionation process, and an attempt to solve such problem, by lowering the filtration rate, has been made by employing an emulsifier such as a polyglycerol ester of a fatty acid (JP-A-11-106782).